getting new prop tight enough

[benwa43]

I recently hit a submerged log at idle and put a dog ear in one blade of my prop. I installed a new prop but it has a tiny amount of play in it and there is a little vibration in the boat. I can't imagine I did any damage to the prop shaft hitting the log at such slow speed. The problem is that I can't tighten the nut any tighter. I followed the directions - slide prop on shaft without key and mark. Install key and slide prop on and check mark. It lines up. I didn't block the prop at all when tightening for fear of bending the prop. Any suggestions for getting the prop tighter and eliminating that little bit of play between the prop and shaft?

[SGY]

RE: getting new prop tight enough

Block it. You won't bend it. I read somewhere that you need at least 30 lbs of torque on that nut.

[DavidF]

RE: getting new prop tight enough

The vibration is coming from the prop not being tight on the shaft. Sounds like the nut is running out of threads on the shaft and/or the key is too long. Make sure the key is not too long and then put one or more stainless steel washer under the nut. The prop CANNOT be loose on the shaft.

One method for getting the nut tight enough is to place wrench on nut, hold prop with gloved hand, hit wrench sharply with dead blow hammer (a couple of times).

[JoeCos]

RE: getting new prop tight enough

Like what SGY said - use a wood block, wedge the prop good and solid. If you have a Breaker Bar, coupled with 1 1/16 size socket (i think) sure will help , then get a good leveraging angle, then crank that thing good !

[derby]

I think this is why you need torches to get your props off. You shouldnt need a hammer or a block of wood to put on a prop.

If you adjust the key properly the prop should slide on and only require 30-40 ft-lbs to tighten.

2 cents over and out!

[M3Fan]

I don't see how a prop on an inboard could be loose after hitting the throttle on the water, even without a nut at all... I've always been of the school that once that prop pushes the 2400lb+ boat forward a few times against that tapered surface, the nut is only there as a "secondary" measure of holding the prop on, should it break loose. My prop nut is actually a bit loose, held in place by the cotter pin. This is because even though I cranked it down, as soon as I actually used the prop and it seated under 1000's of lbs of load the nut was loose again. I'll probably crank it down again but it was loose when I took it off last as well, and I'm assuming a dealer installed the last prop. It's not on the top of my priority list. Theoretically I'm thinking with that prop turning forward, and pushing against the tapered surface, that guy isn't going anywhere. Even if it did break loose, the key will keep it from turning against the nut and possibly causing the nut to unscrew. I could be completely wrong, but it would be another great topic for Boat Mythbusters, if I ever create the website.

[todda]

Hey Benwa, for piece of mind, another alternative to the nut/cotter-pin method, is to buy a stainless nut that has the nylon insert (usually called "nylocks"). When I did this to my 99 SNOB, it relieved all the prop rattle that I had. It is nice an tight, and no noise what-so-ever. I keep my old prop nut and cotter pin in my boat for anytime I might need it, but this method has worked well for me.

Todd

[benwa43]

My original thinking was along the lines of M3Fan's since the castle nut was relatively loose when I tookk the damaged prop off. The new prop would not slide on the shaft quite as far as the old one but the difference wasn't much and I figured it would "seat" itself after some use. Now after skiing about half a dozen times, the prop still has play in it. I will try to tighten it more and if that doesn't work I will track down a nylock nut.

[M3Fan]

My original thinking was along the lines of M3Fan's since the castle nut was relatively loose when I tookk the damaged prop off. The new prop would not slide on the shaft quite as far as the old one but the difference wasn't much and I figured it would "seat" itself after some use. Now after skiing about half a dozen times, the prop still has play in it. I will try to tighten it more and if that doesn't work I will track down a nylock nut.

There goes my theory.... better tighten that nut.

[jasper]

M3Fan, your theory may be correct, but your it also works (or doesn't work) when you put the throttle in reverse.

I'd stay away from the Nylock nut. I'd stay away from any stainless nut on a stainless shaft. Use a brass castle nut. Stainless on stainless can lock-up.

jasper

[derby]

I'll second the stainless and stainless, but not the hammer.

[JoeCos]

Dont forget to apply a small dab of anti-seize grease on the shaft, key, and nut.

[skijones]

As one who has lost a prop, the only time you put pressure on the nut is in reverse or backing down quick. I lost mine at the end of a run(brand new prop, first run of the year, after coming back after knee surgery). Ended up skiing behind my dads pontoon.

Seat the prop and get a chunk of pine 4x4, put it between the hull and the prop and tighten "good and tight". Line up the holes for the cotter key(do not back off the nut), install cotter key and bend over both ways.

Nylock nuts are great, for one use. Use a stainless cotter key and don't hit stuff in the water(easier said than done).

[DavidF]

Nylock nuts are fine, but convention says to also use the cotter pin in the event nylock nut decides to let go. the pin will keep the nut from completely backing off. The way I read the original post was that even after tightening the nut, the prop was loose. If this is the case, then the nut is bottoming out on the threads (or in other words, there is not enough threads on the shaft). If this is the case all the tightening in the world will not fix the prop rattle.

Also, the forward thrust from the prop on the shaft is not enough to keep the prop in place. Cutting power or backing down is enough force to cause the prop to break loose from the seated position. Thus if you back off the castle nut to find a slot for the cotter pin, you can have a resultant vibration from the prop being loose. Forward thrust is not enough to reseat the prop. I know this because on my new shaft/prop nut setup, I had this problem. Basically, the castle nut I bought was too short. I tightened the nut to 60 ft-lbs. First outing and all was well until about two or three power cuts from speed, then the vibration set-in. Dove in and the nut had backed off and the prop was loose. Once loose, the vibration would not go away. A taller castle nut fixed the issue.

[benwa43]

I might have been a little unclear in my original post. The nut is not bottoming out on the threads, I just can't turn it anymore without spinning the shaft. I haven't gotten a chance to try the block yet to see if I can crank it down.